Solvent deasphalting of heavy residual hydrocarbon containing feedstocks such as vacuum and atmospheric resids is well known in the art and extensively used in modern petroleum and petrochemical processing of crude oils and other raw petroleum refining feedstocks. As the need for processing lower grade feedstocks with lower API gravities and higher viscosities in existing and new petroleum refining facilities increases, the increase on petroleum resid content and overall residual production continues to require improved and/or larger facilities for subsequent treatment of these residual intermediate products produced.
The refining residual products, including atmospheric and vacuum resids, have high boiling point ranges, with initial boiling points ranging from about 650° F. (343° C.) to over 1000° F. (538° C.), as well as high density, viscosity, and asphaltene metal contents. For many refinery processes, a significant amount of the high molecular weight multi-ring asphaltene components must be removed from these residual streams prior to further processing these streams into higher value products. Solvent deasphalting processes such as Propane Deasphalting (PDA), Solvent Deasphalting (SDA), and Residual Oil Solvent Deasphalting (ROSE) are well known in the art. All of these processes use low boiling-point, alkane-based solvents to precipitate the asphaltenes from the resid/solvent mixture and to remove a higher asphaltene content product stream as well as a lower asphaltene content oil/solvent stream. It should be noted that the term solvent deasphalting used herein, pertains to any extraction deasphalting process that utilizes an alkane-based solvent for the extraction of asphaltenes. The lower boiling point solvent is recovered from the low asphaltene content oil/solvent stream to produce a deasphalted oil (“DAO”) with reduced asphaltene content. Depending upon the specifications for the solvent deasphalting process, the DAO product produced is of a reduced asphaltene sufficient to be utilized as a feedstock to subsequent refinery upgrading processes. The DAO product thus produced is generally of sufficient quality to be sent for further processing in refining catalytic upgrading units, but the DAO product is most commonly utilized in the production of lubrication oil grade products.
Several patents exist to improve the solvent deasphalting processes. U.S. Pat. No. 3,929,616 describes a process for solvent extraction of aromatics from a residual oil prior to hydrocracking and solvent deasphalting. U.S. Pat. Nos. 4,592,832 and 5,178,750 describe processes for improving the deasphalting process through a two-step solvent process. Other patents, such as U.S. Pat. No. 6,274,030 have utilized filters to remove solids in conjunction with the solvent deasphalting, but the process does not appreciably change the molecular composition of the hydrocarbon stream produced. U.S. Pat. No. 6,524,469 utilizes a membrane separations process to upgrade a visbroken resid stream prior to solvent deasphalting. However, all of these processes require either additional available capacity in the solvent deasphalting unit and/or the use of additional solvents, in particular valuable low boiling point alkane-based solvents, for the pre-treatment of the heavy oil stream prior to the solvent deasphalting process.
There are many problems that exist in the industry subject to the need for improved deasphalting processes. Firstly, conventional solvent deasphalting processes are expensive to install and operate. They require a significant amount of process equipment and require the use of valuable hydrocarbon based solvents which can be lost in the processing of the residual oils, as well as a significant amount of energy expenditures in order to fractionate and recover the solvent components from the deasphalted oil components. Additionally, refineries in the U.S. as well as many other countries are aging and struggling to maintain or increase capacity while the demand to utilize raw petroleum feedstocks with higher residual contents is increasing. Existing solvent deasphalting units can be difficult to upgrade especially if the deasphalting units are hydraulically limited. In this case, the equipment is too small for the required production rates, and expensive equipment replacement or modifications can be prohibitive in costs. Thirdly, as the demand for more and higher quality lube oil products increases, existing solvent deasphalting units are faced with need to produce both a higher quality product as well as an increase in production. As stated, today's petroleum refiner is faced with very costly modifications to existing deasphalting units to meet these increased quality and production volume demands.
Therefore, there is a need in the industry for an improved integrated deasphalting process. An even greater need exists for a process which can improve the product quality and production throughput of DAO from existing solvent deasphalting units while utilizing equipment which can be operated in conjunction with existing deasphalting processes, and which do not require significant equipment replacements or modifications to an existing deasphalting unit.